Electrically ignited pilot burner



Sept. 29, 1964 E. C. MILLER ELECTRICALLY IGNITED PILOT BURNER Filed June27, 1961 EARLE 6. MILLER INVENTOR United States Patent 3,150,710ELECTRICALLY IGNITED PiLOT BURNER Earle C. Miller, Worcester, Mass.,assignor to Riley Stoker Corporation, Worcester, Mass., a corporation ofMassachusetts.

Filed June 2 7, 1961, Ser. No. 127,781 8 Claims. (Cl. 158-115) Thisinvention relates to an ignitor and more particularly to apparatusarranged to provide a continuous flame for the ignition of the burner ofa furna'ce.

In the burning of fuel and particularly of pulverized coal, it is commonpractice to provide a small flame or pilot which burns continuously andwhich uses a fuel which is less likely to blow out. It is necessary toprovide some means for igniting the pilot in turn and for maintaining itin a lighted condition at all times. At the present time, it is theusual practice to use an ignitable gasas the pilot fuel and to use anelectric spark as the ignition means. Some of the problems presented bythe provision of such a pilot are solved by the invention set forth inthe patent of Thomasian et al. No. 3,007,084 issued October 31, 1961 andin the application of Miller, Serial Number 717,949 filed February 27,1958, and now abandoned. Although these ignitors usually operateadequately, there are some conditions under which they are not entirelysatisfactory. Among other things, the supporting of a high-voltageelongated electrode of the type shown in these applications presents aproblem in that the supports are ceramic insulators and considerablediificulty has been experienced with the breakage of the insulators andshorting of the electrodes. Furthermore, having the electrodes at theend of the gun where they are exposed to the furnace radiation leads tosome deterioration of the electrodes and subsequent shorting. These andother difficulties experienced with the prior art devices have beenobivated in a novel manner by the present invention.

It is, therefore, an outstanding object of the present invention toprovide an ignitor for use in a furnace burner wherein flame stabilityis maintained despite high air velocity. I

It is another object of this invention to provide an ignitor in whichgas passing between electrical electrodes is maintained in a readilyignitable condition despite variations in air velocity passing over theoutside of the ignitor.

Another object of the invention is the provision of a gas-electricignitor in which the electrodes are supported in such a manner "that thegun may be subjected to rough usage without breakage of delicate parts.

Another object of the invention is the provision of a gas electricigntor which may be readily removed for inspection and maintenance.

It is a still further obectof the invention to provide a gas-electricignitor having an electrode arrangement which is not subject todeterioration and shorting due to exposure to heat or due to beingmounted in delicate insulating supports.

Although the novel features which are believed to be characteristic ofthis invention will be particularly pointed out in the claims appendedhereto, the invention itself, as to its objects and advantages, the modeof its operation, and the manner of its organization may be bestunderstood by referring to the following description taken in'connection with the accompanying drawing forming a part thereof inwhich: a V

The single figureis a longitudinal sectional view of an ignitorembodying the principles of the present invention.

The ignitor, indicated generally by the reference numeral 10, is shownas mounted on a wall llof a burner. The wall is formed with a circularaperture 12 in which 3,150,710 Sept. 29, 1964 is inserted an insulatingplug 13 which, in turn, has a circular aperture 14. Residing in theaperture 14 is an outer tube 15 to which is fastened by welding a collar16 which is bolted to the wall 11 on the outer surface thereof. Theouter tube 15 extends well into the burner housing and has connectedthereto, in the vicinity of the wall 11, a threaded fitting 17';fastened in the fitting is a pipe 18 leading to a portion of the burnerhaving a more or less constant air pressure. This portion wouldpreferably be the burner ducting outside of the burner vanes, this beingan area which has a continuously-high static air pressure. v

The outer tube 15 also extends "outwardly of the wall 11 a considerable"distance and its outer end is provided with diametrically-opposed ears19 and 21 having hingedly connected thereto swinging bolts 22 and 23provided with wing nuts 24 and 25, respectively. An annular sealing ring26 fits snugly around an intermediate tube 27 which is slidable withinthe outer tube 15. The ring is provided with a longitudinal flange 28which embraces a resilient seal or packing 29. The bolts 22 and 23 liein slotted ears 31 and 32 extending outwardly from the ring 26 and thering and its packing 29 are pressed tightly by wing nuts against theouter end of the outer tube 15 and inwardly against the outer surface ofthe intermediate tube 27. The intermeditae tube 27 has a length in theorder of the length between the outer end of the inner tube 15 and thefitting 17; at its outer end the intermediate tube is provided with afitting 33. The intermediate tube 27 is welded to the fitting 33;threaded into the fitting concentrically of the intermediate tube is aninner tube 34 which has an external diameterconsiderably smaller thanthe internal diameter of the intermediate tube 27, thus definingtherebetween an annular space 35. Threaded into the fitting 33concentric with and at the opposite side of the inner tube 34 is a sparkplug 36 having an insulating neck 37 from which extends an elongatedelectrode 38.

The electrode is exactly concentric with the inner tube 34. At its outerend the spark plug 36 is fastened to a cable 39 by which it is connectedto a high voltage alternating current source (not shown). The fitting 33is provided with an inner chamber 41 into which the spark plug 36extends and into which the inner tube 34 extends. A gas conduit 42 isthreaded to the fitting at a right angle to the inner tube 34 and entersthe chamber 41, the conduit being connected at the other end to a sourceof gas (not shown). A disc-like wall 43 extends across the inner tube 34adjacent the fitting 33 and it is provided with a central aperture 44through which the electrode 38 extends, the aperture being larger thanthe electrode to define an orifice therebetween. Closely adjacent thewall 43 and on the side thereof opposite the fitting 33 are located aseries of apertures 45 through the wall of the tube. Further away fromthe wall are a set of three radial electrodes 46 which are fastened inthe wall of the tube 34 and extend radially inwardly to Within adefinite distance of the electrode 38; these are the ground electrodes,while the electrode 38 would normally be at a high voltage. V 7

At the end of the inner tube 34which lies close to the furnace it isprovided with a cup 47 whichis considerably larger in diameter than theinner tube 34, but does not have an external diameter larger than theinner diameter of the outer tube 15. A perforated plate 48 extendsacross the cup. The inner tube is provided between the cup 47 and theouter end with a collar '49 which is capable of sliding smoothly withintheouterft'ube 15 and which is provided with set screws for fastening itfirmly to the inner tube 34. This collar is normally located closer tothe furnace than the fitting 17, that is to say, farther away from theWall 11. A set screw 51 extends through the outer" tube and pressesagainst the intermediate tube 27 to lock it in place and prevent slidingtherebetween. Also hingedly mounted in the ears 19 is an L-shaped rod 58to which is welded a closure 59 which exactly fits over the outer end ofthe outer tube 15.

The operation of the invention will now be readily understood in view ofthe above description. Gas enters the ignitor through the conduit 42passing into the chamber 41 and then out again into the tube 34. The gaspasses through the aperture 44 of the wall 43 through the annular areabetween the edge of the aperture and the surface of the electrode 38.Air enters the ignitor through the pipe 18 and passes into the outertube 15 and, then, into the annular space between the outside of theinner tube 34 and the inside of the intermediate tube 27. Air cannotleave in the direction of the furnace along the inside of the tube 15because the collar 49 effectively closes that end of the tube. Air doespass outwardly to the space outside of the inner tube 34 in which theapertures are located. The air moves radially inwardly through theseapertures toward the stream of gas surrounding the electrode 38. Thisgas moves axially while the air from the apertures 45 is moving radiallyinwardly. When they meet, thorough mixing takes place before they passaxially together along the electrode 38 and, eventually, between theelectrode 38 and the radial electrodes 46. Now, the electrodes 46 areconnected to ground voltage back through the frame of the gun ignitor;the electrode 38 is connected to the high-voltage alternating currentsource through the cable 39. Sparking takes place, therefore, betweenthe electrode 38 and the electrodes 45. When the gas-air mixture passesbetween these electrodes and sparking takes place, the gas will beignited. The ignited mixture passes downwardly through the inner tube34, through the aperture plate 48 of the cup 47, and forms a flame atthe end of the ignitor. The introduction of the air radially through theaperture 45 and meeting the gas at right angles promotes a thoroughmixing which tends to make the ignitor flame more stable. The provisionof a cup and apertured plate 48 at the outer end of the gun tends toprevent the flame from being blown out by the air in the main burneritself, since the cap 47 acts as a flame holder. When it is desired toremove the operating elements of the ignitor, this is done by looseningthe set screw 51. The intermediate tube 27 and the inner tube 34 may bemoved outwardly of the outer tube 15. Before they are removed, however,it is necessary to loosen the packing 29 by loosening the nuts 28. Then,the intermediate tube may be withdrawn, carrying the rest of theelements with it. In order to close the outer end of the outer tube 15it is necessary to remove the ring 28 and the packing 29. For thispurpose the bolts 22 and 23 are rotated laterally so that they and theirnuts 24 and 25 are free of the ears 31 and 32, respectively. The ring isthen free to be lifted away from the pipe and at that time the closure59 may be moved into place to close the end of the pipe. In this wayneither gas from the furnace nor air from the conduit 18 will flow intothe boiler room.

While certain novel features of the invention have been shown anddescribed and are pointed out in the annexed claims, it will beunderstood that various omissions, substitutions and changes in theforms and details of the device illustrated and in its operation may bemade by those skilled in the art without departing from the :spirit ofthe invention.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

1. An ignitor for furnace having a burner wall and an air box,comprising an outer tube adapted to extend through the burner wall andto be fastened thereto, an intermediate tube slidable within the outertube and having a fitting attached to its outer end for introducing acombustible gas therein, the fitting also holding an electrode coaxiallyof the tubes, an inner tube held in the fitting and extending coaxiallyof the intermediate tube, the inner tube having an external diameterwhich is smaller than the internal diameter of the intermediate tubewhereby a substantial space exists therebetween, means supplying thespace with pressure air, electrodes extending radially inwardly of theinner tube to positions adjacent the electrode, and apertures throughthe inner tube adjacent the electrodes.

2. An ignitor for furnace having a burner wall and an air box,comprising an outer tube adapted to extend through the burner wall andto be fastened thereto, means for connecting the outer tube to the airbox, a closure fastened to the outer tube so as to lie externally of thefurnace wall and capable of closing the external end of the tube onoccasion, an intermediate tube slidable within the outer tube and havinga fitting attached to its outer end for inroducing a combustible gastherein, the fitting also holding an elongated electrode coaxially ofthe tubes, an inner tube held in the fitting and extending coaxially ofthe intermediate tube, the inner tube having an external diameter whichis smaller than the internal diameter of the intermediate tube whereby asubstantial space exists therebetween, a wall across the inner tubehaving a central aperture through which the elongated electrode extends,electrodes extending radially inwardly of the inner tube to positionsadjacent the elongated electrode, and apertures through the inner tubeadjacent the electrodes.

3. An ignitor for furnace having a burner wall and an air box comprisingan outer tube adapted to extend through the burner wall and to befastened thereto, means for connecting the outer tube to the air box, aclosure fastened to the outer tube so as to lie externally of thefurnace wall and capable of closing the external end of the tube onoccasion, an intermediate tube slidable within the outer tube andconsiderably shorter than the outer tube, the intermediate tube having afitting attached to its outer end for introducing a combustible gastherein, the fitting also holding an elongated electrode coaxially ofthe tubes, an inner tube held in the fitting and extending coaxially ofthe intermediate tube, the inner tube having an external diameter whichis smaller than the internal diameter of the intermediate tube whereby asubstantial space exists therebetween, a collar extending between theinner and outer tubes, electrodes extending radially inwardly of theinner tube to positions adjacent the elongated electrode, and aperturesthrough the inner tube adjacent the electrodes.

4. An ignitor for furnace having a burner wall and an air box,comprising an outer tube adapted to extend through the burner wall andto be fastened thereto, the outer tube being adapted to have one endoutside of the Wall and another end inside the wall, means forconnecting the outer tube to the air box, a closure fastened to theouter tube so as to lie externally of the furnace wall and capable ofclosing the external end of the tube on occasion, an intermediate tubeslidable within the outer tube and having a fitting attached to itsouter end for introducing a combustible gas therein, the fitting alsoholding an elongated electrode coaxially of the tubes, a seal betweenthe end of the outer tube which is adapted to lie outside the wall andthe outer surface of the intermediate tube, an inner tube held in thefitting and extending coaxially of the intermediate tube, the inner tubehaving an external diameter which is smaller than the internal diameterof the intermediate tube whereby a substantial spacing existstherebetween, a cup-like flame holder on the inner end of the innertube, electrodes extending radially inwardly of the inner tube topositions adjacent the elongated electrode, and apertures through theinner tube adjacent the electrodes.

5. An ignitor for furnace having a burner wall and an air box,comprising an outer tube adapted to extend through the burner Wall andto be fastened thereto, means for connecting the outer tube to the airbox, a closure fastened to the outer tube so as to lie externally of thefurnace wall and capable of closing the external end of the tube onoccasion, an intermediate tube slidable within the outer tube andconsiderably shorter than the outer tube, the intermediate tube having afitting attached to its outer end for introducing a combustible gastherein, the fitting also holding an elongated electrode coaxially ofthe tubes, an inner tube held in the fitting and extending coaxially ofthe intermediate tube, the inner tube having an external diameter whichis smaller than the internal diameter of the intermediate tube whereby asubstantial space exists therebetween, a collar extending between theinner and outer tubes, a wall across the inner tube having a centralaperture through which the elongated electrode extends, electrodesextending radially inwardly of the inner tube to positions adjacent theelongated electrode, and apertures through the inner tube adjacent theelectrodes.

6. An ignitor for furnace having a burner wall and an air box,comprising an outer tube adapted to extend through the burner wall andto be fastened thereto, the outer tube being adapted to have one endoutside of the wall and another end inside of the wall, means forconnecting the outer tube to the air box, a closure fastened to theouter tube so as to lie externally of the furnace wall and capable ofclosing the external end of the tube on occasion, an intermediate tubeslidable within the outer tube and considerably shorter than the outertube, the intermediate tube having a fitting attached to its outer endfor introducing a combustible gas therein, the fitting also holding anelongated electrode coaxially of the tubes, a seal between the end ofthe outer tube which is adapted to lie outside the wall and the outersurface of the intermediate tube, an inner tube held in the fitting andextending coaxially of the intermediate tube, the inner tube having anexternal diameter which is smaller than the internal diameter of theintermediate tube whereby a substantial space exists therebetween, acollar extending between the inner and outer tube, a cup-like flameholder on the inner end of the inner tube, electrodes extending radiallyinwardly of the inner tube to positions adjacent the elongatedelectrode, and apertures through the inner tube adjacent the electrodes.

7. An ignitor for furnace having a burner wall and an air box,comprising an outer tube adapted to extend through the burner wall andto be fastened thereto, the outer tube having adapted to have one endoutside of the wall and another end inside the wall, means forconnecting the outer tube to the air box, a closure fastened to theouter tube so as to lie externally of the furnace wall and capable ofclosing the external end of the tube on occasion, an intermediate tubeslidable within the outer tube and having a fitting attached to itsouter end for introducing a combustible gas therein, the fitting alsoholding an elongated electrode coaxially of the tubes, a seal betweenthe end of the outer tube which is adapted to lie outside the wall andthe outer surface of the intermediate tube, an inner tube held in thefitting and extending coaxially of the intermediate tube, the inner tubehaving an external diameter which is smaller than the internal diameterof the intermediate tube whereby a substantial space existstherebetween, a wall across the inner tube having a central aperturethrough which the elongated electrode extends, a cuplike flame holder onthe inner end of the inner tube, electrodes extending radially inwardlyof the inner tube to positions adjacent the elongated electrode, andapertures through the inner tube adjacent the electrodes and on theinner side of the wall.

8. An ignitor for furnace having a burner Wall and an air box,comprising an outer tube adapted to extend through the burner wall andto be fastened thereto, the outer tube being adapted to have one endoutside of the wall and the other end inside the wall, means forconnecting the outer tube to the air box, a closure fastened to theouter tube so as to lie externally of the furnace wall and capable ofclosing the external end of the tube on occasion, an intermediate tubeslidable within the outer tube and considerably shorter than the outertube, the intermediate tube having a fitting attached to its outer endfor introducing a combustible gas therein, the fitting also holding anelongated electrode coaxially of the tubes, a seal between the end ofthe outer tube which is adapted to lie outside the wall and the outersurface of the intermediate tube, an inner tube held in the fitting andextending coaxially of the intermediate tube, the inner tube having anexternal diameter which is smaller than the internal diameter of theintermediate tube whereby a substantial space exists therebetween, acollar extending between the inner and outer tubes, a wall across theinner tube having a central aperture through which the elongatedelectrode extends, a cuplike flame holder on the inner end of the innertube, electrodes extending radially inwardly of the inner tube topositions adjacent the elongated electrode, and apertures through theinner tube adjacent the electrodes and on the inner side of the wall.

References Cited in the file of this patent UNITED STATES PATENTS2,241,295 Clark May 6, 1941 2,880,792 Raskin Apr. 7, 1959 FOREIGNPATENTS 499,657 Germany June 14, 1930

1. AN IGNITOR FOR FURNACE HAVING A BURNER WALL AND AN AIR BOX,COMPRISING AN OUTER TUBE ADAPTED TO EXTEND THROUGH THE BURNER WALL ANDTO BE FASTENED THERETO, AN INTERMEDIATE TUBE SLIDABLE WITHIN THE OUTERTUBE AND HAVING A FITTING ATTACHED TO ITS OUTER END FOR INTRODUCING ACOMBUSTIBLE GAS THEREIN, THE FITTING ALSO HOLDING AN ELECTRODE COAXIALLYOF THE TUBES, AN INNER TUBE HELD IN THE FITTING AND EXTENDING COAXIALLYOF THE INTERMEDIATE TUBE, THE INNER TUBE HAVING AN EXTERNAL DIAMETERWHICH IS SMALLER THAN THE INTERNAL DIAMETER OF THE INTERMEDIATE TUBEWHEREBY A SUBSTANTIAL SPACE EXISTS THEREBETWEEN, MEANS SUPPLYING THESPACE WITH PRESSURE AIR, ELECTRODES EXTENDING RADIALLY INWARDLY OF THEINNER TUBE TO POSITIONS ADJACENT THE ELECTRODE, AND APERTURES THROUGHTHE INNER TUBE ADJACENT THE ELECTRODES.